You could opt to build a Litecoin mining rig instead of a Bitcoin miner, though. A single ATI Radeon 7950 will net you approx. 630 kH/s mining LTC, which according to
http://dustcoin.com/mining will net you approximately $199.13 in profit per month minus your cost of electricity. This is as of Tuesday April 30th, 2013 at 3:45 AM (GMT -4) (just for reference). If you go over to
https://btc-e.com/ you can find the current exchange rate for both BTC and LTC, and some other smaller derivative coins. Right now LTC/USD is at $4.16. I bought $20 of it a week or so ago back when it was $2.59. It's considerably appreciated since then, and lots of people expect LTC to go up and up.
So, basically what I'm saying is, LTC is more profitable to mine than LTC even without assuming an appreciation in value, and an appreciation in value is highly likely when Mt. Gox starts trading LTC. A lot of the people in the BTC-E trollbox (the chat box on the right hand side of BTC-E's website), and also in /r/litecoin and /r/litecoinmining on Reddit speculate that Mt. Gox will begin trading in LTC. Mt. Gox has actually commented on this themselves in a press release, saying something about their plans regarding LTC. This caused the recent price jump which happened almost overnight from $2.50 to over $4 a coin amid the rumours.
Personally, I feel that in the coming months a lot of Bitcoin miners who have GPU based Bitcoin miners will switch over to Litecoin because they will start to see the decreased profitability of mining Bitcoin with a GPU especially amid the new FPGA/ASIC based Bitcoin miners which are much more energy efficient and have much higher returns on investment.
As per your specs that you posted in your first post, I too am trying to come up with a suitable build to get this miner of mine up and running. My budget right now is approximately $1000, so I'll only be able to afford one 7950 (or other GPU that I decide to go for instead; but I'll probably go for the 7950) initially, on top of a decent 80-Plus Platinum PSU and also a Phenom II X4 965 in lieu of the Sempron (I had that in there too, but I ultimately decided against it because I want to use this as a fileserver as well, and I want to possibly be able to resell it later as well).
Here's my wishlist so far on Newegg:
http://secure.newegg.ca/WishList/PublicWishDetail.aspx?WishListNumber=22932806Feel free to take a look. It's based heavily off of
http://www.cryptobadger.com/2013/04/build-a-litecoin-mining-rig-hardware/ which is a /very/ well written (in my opinion) and recently written guide on how to get started building a good, decent mining rig.
The only things I worry about are the following: I worry if the PSU is worth it/is overkill for the price/whether I should be going for a less-efficient less-expensive PSU but of comparable wattage. I wonder how much it'll really save me at the wall in terms of electricity costs. I also wonder if I should indeed be springing for a Radeon 7970 instead of a 7950, but all of the sources I've read say that the 7950 is the way to go in terms of the hashrate/$ ratio.
